Oscillator circuits play a key role in integrated circuit design. Almost all digital cores needs, for example, a clock generator to enable the operation of the circuit. There are many different possibilities for designing an oscillator. A precise oscillator may be built up with quartz. However, a quartz is an expensive external component which cannot be integrated on the same silicon as the rest of the circuitry. Another drawback of such quartz oscillators is the limited temperature range, for example a temperature range from −40° to +125° C. However, many applications need an extended temperature range from, for example, −40° to +170° C.
To make an oscillator circuit inexpensive, external components should be avoided. A CMOS oscillator may be embedded in an integrated circuit design. There are different ways to design fully integrated CMOS oscillators. The most important parameters are a low temperature drift of the output frequency, a low power consumption, a low clock jitter, a good power supply rejection ratio, a low voltage ripple on the power supply, a low charge injection in the substrate, and a small area consumption.
There is a need to provide an oscillator circuit which enables a reliable generation of a stable output frequency in addition to lower power and small area consumption.